Coated articles

ABSTRACT

Multilayer high transmittance, low emissivity coatings on transparent substrates feature a special antireflective base film of at least two parts on the substrate-near side of a metallic, reflective film. A first of the two parts is in contact with the metallic film. This first film-part has crystalline properties for causing the metallic film to deposit in a low resistivity configuration. The second of the two film-parts supports the first part and is preferably amorphous. Coated articles of the invention also feature, in combination with the above-mentioned base film or independently thereof, a newly discovered, particularly advantageous subrange of thicker primer films for coated glass that can be thermally processed for tempering, heat strengthening, or bending.

This application claims the benefit of U.S. Provisional Application No.60/015,718 filed Apr. 25, 1996.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the art of multilayered filmsor coatings providing high transmittance and low emissivity, to articlescoated with such films or coatings, and more particularly to suchcoatings or films formed of metal and metal oxides and deposited ontransparent substrates.

2. Discussion of the Presently Available Technology

High transmittance, low emissivity films or coatings generally include areflective metal film or layer which provides infrared reflectance andlow emissivity, sandwiched between dielectric, antireflective films orlayers of metal oxides to reduce the visible reflectance. Thesemultilayer coatings are typically produced by cathode sputtering,especially magnetron sputtering.

U.S. Pat. No. 4,610,771 to Gillery provides a film composition of anoxide of a zinc-tin alloy, as well as multiple-layer films of silver andzinc-tin alloy oxide layers for use as a high transmittance, lowemissivity coating. This oxide film may have the composition of zincstannate (Zn₂ SnO₄), but may also range from that exact composition.

U.S. Pat. No. 4,806,220 to Finley discloses a multilayer film coatingsuitable for high temperature processing. A type of this coatingutilizes metal primer layers e.g. titanium primer layer both above andbelow a reflective metal layer of greater thickness than usual, up to 50Angstroms in thickness.

It would be desirable to produce high transmittance films and articlecoated with such films that have minimal emissivity, low electricalresistivity and improved shear resistance, which exhibit improvedresistance to weathering and can withstand high temperature processingwhere the use of a titanium primer layer below the reflective metallayer may be avoided. Alternatively, in the case where more than onereflective metal layer is present, it would be desirable to avoid theuse of a titanium primer adjacent the substrate-near side of any of thereflective metal layers.

SUMMARY OF THE INVENTION

The present invention is directed to multilayer high transmittance, lowemissivity coatings on transparent substrates which feature anantireflective base film of at least two parts on the substrate-nearside of a metallic, reflective film, that is to say the side of themetallic reflective film that is in parallel facing relationship withthe substrate. A first of the two parts is in contact with the metallicfilm. This first film-part has crystalline properties for causing themetallic film to deposit in a low resistivity structure. The second ofthe two film-parts supports the first part and is of a chemically andthermally more durable, preferably amorphous, material. The presentinvention includes both coatings having a single metallic reflectivefilm and coatings with multiple metallic, reflective films, in whichcase the novel base film of the present invention can be utilized forjust one of the multiple metallic films, for several or for all of them.

More particularly the present invention is directed to a hightransmittance, low emissivity coated article having:

a transparent, nonmetallic substrate;

a dielectric, antireflective base film deposited over the substrate, thebase film including a crystalline metal-contacting film-part and asupport film-part where the support film-part is over and may be incontact with the substrate and wherein the support film-part includes amaterial other than the crystalline metal-contacting film-part;

a metallic reflective film deposited on the crystalline metal-contactingfilm-part of the base film;

a primer film deposited on the metallic reflective film; and

a dielectric, antireflective film deposited on the primer film.

In an alternative embodiment of the present invention, an exteriorprotective overcoat layer is deposited on the dielectric, antireflectivefilm.

In a preferred embodiment of the present invention, the transparent,nonmetallic substrate is glass, the support film-part is a zinc stannatefilm, the crystalline metal-contacting film-part is a zinc oxide film;the metallic reflective film is a silver film, the primer film isdeposited as titanium metal, the dielectric, antireflective film is azinc stannate film, and the exterior protective overcoat layer is atitanium oxide film.

Coated articles of the invention also feature, in combination with theabove-mentioned base film or independently thereof, a newly discovered,particularly advantageous subrange of the thicker primer layers, orfilms, of the above-referenced U.S. Pat. No. 4,806,220 to Finley.

NOMENCLATURE AND MEASUREMENT TECHNIQUES

When referring to crystal planes herein, representation of the planarindices within braces, i.e. {}, is a reference to all planes of thatform. This convention is explained, for instance, in Cullity's "Elementsof X-Ray Diffraction", Addison-Wesley, 1956, pages 37-42.

Gas percentages herein are on a flow (volume/unit time, standard cubiccentimeters per minute ("SCCM")basis.

Disclosed thicknesses of the various layers of the multiple layeredcoatings of the present invention herein are determined on the basis oftwo different procedures, depending on whether layer is a dielectriclayer or a metal layer.

The thickness of dielectric layers, or films, is determined by the aidof a commercial stylus profiler (hereinafter referred to as the "StylusMethod"), as follows. Before the deposition of each layer, a narrow lineis drawn on the glass substrate with an acetone soluble ink. Followingthe deposition of the coating the line, and that portion of the coatingdeposited over it, is removed by wetting the surface with acetone andgently wiping with laboratory tissue. This creates a well-defined stepon the surface of the glass whose height is equal to the thickness ofthe layer and can be measured with a profiler.

Two potential complications make the Stylus Method used for measuringthe thickness of dielectric layers less favorable for measuring thethickness of thin metal films. First, metals, such as titanium andsilver, are more prone to abrasion when wiped. Second, metals reactreadily with the ambient atmosphere when removed from a vacuum chamber.Both of these phenomena can result in significant errors if thicknessmeasurements are made via the Stylus Method.

As an alternative, a method that will be referred to as the "XRF Method"herein is used to measure the thickness of metal layers. The XRF methoduses a calibrated x-ray fluorescence instrument to measure the weight ofthe metal per unit area of the coating (namely, in μg/cm²). The XRFmethod makes the assumption that the metal film is as dense as its bulkform. With this assumption, the metal film's measured weight per unitarea is then converted to a thickness in Angstroms, using its bulkdensity.

For completeness sake, it should be noted that sputtered metal films areoften less dense than their corresponding bulk metals, so that abovedescribed assumption is not always precisely correct, and the XRF Methodmay in some cases underestimate the thickness of the metal film due tothis variation in density. Thus, for the thin metal films, the initialmeasurement of weight per unit area (μg/cm²) is more accurate than thecorresponding conversion to thickness based upon bulk density.Nonetheless, the XRF Method provides a useful approximation forcomparing the relative thicknesses of the layers in a coating. Thicknesstolerances given herein represent twice the standard deviation of themeasurements.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a plot which shows the effect of primer thickness on shearresistance and visible light transmittance for a multilayered film withamorphous zinc stannate contacting the substrate-near side of silver,before and after heat treatment.

FIG. 1B is a plot which shows the effect of primer thickness on shearresistance and visible light transmittance for a multilayered film withcrystalline zinc oxide contacting the substrate-near side of silverbefore and after heat treatment.

FIG. 2A is a plot which shows the effect of primer thickness on shearresistance and sheet electrical resistance for a multilayered film withamorphous zinc stannate contacting the substrate-near side of silver,before and after heat treatment.

FIG. 2B is a plot which shows the effect of primer thickness on shearresistance and sheet electrical resistance for a multilayered film withcrystalline zinc oxide contacting the substrate-near side of silver,before and after heat treatment.

FIG. 3 is a plot which compares the haze rating versus primer thicknessof a multilayered film with crystalline zinc oxide contacting thesubstrate-near side of silver with a multilayered film with amorphouszinc stannate contacting the substrate near side of silver.

FIG. 4A is a plot which shows the before-heat and after-heat grazingangle x-ray diffraction spectra of Sample E of Table 1 wherein the zincoxide metal-contact film-part is not present and the zinc stannate is incontact with the silver.

FIG. 4B is a plot which shows the before-heat and after-heat grazingangle x-ray diffraction spectra of the Sample F in Table 1 wherein thezinc oxide metal-contact film-part is present and is in contact with thesilver. The spectrum of FIG. 48 is also characteristic of the spectra ofSamples A through D in Table 1.

FIG. 5A is a surface plot of results of a before-heat two-variabledesigned experiment that shows the effect on coating electricalresistance of varying thickness of a zinc oxide metal-contact film-partand varying thickness of the titanium primer film.

FIG. 5B is a surface plot of the two-variable experiment of FIG. 5A,showing the after-heat results.

FIG. 6A is a plot of a grazing-angle x-ray diffraction spectrum beforeheating for Sample G of FIG. 9 showing the effect of oxygenconcentration on planar indices formation of a zinc oxide metal-contactfilm-part deposited in an atmosphere of 50% argon and 50% oxygen.

FIG. 6B is a plot of a grazing-angle x-ray diffraction spectrum beforeheating for Sample H of FIG. 9 showing the effect of oxygenconcentration on planar indices formation of a zinc oxide metal-contactfilm-part deposited in an atmosphere of 80% oxygen and 20% argon.

FIG. 6C is a plot of a grazing-angle x-ray diffraction spectrum beforeheating for Sample I of FIG. 9 showing the effect of an amorphousmetal-contact film-part on planar indices formation of a zinc stannatemetal contact film part deposited in an atmosphere of 65% oxygen and 35%argon.

FIG. 6D is a plot of a grazing-angle x-ray diffraction spectrum beforeheating for Sample J of FIG. 9 which was formed under virtuallyidentical conditions is the plot of FIG. 6B and which confirms theresults of the plot of FIG. 6B.

FIG. 7A is a plot of peak intensity of silver {111}, {200} and {220}planes versus silver layer thickness for an amorphous zinc stannatemetal-contact film-part including second order polynomial fits to data,determined by using regression analysis.

FIG. 7B is a plot of peak intensity of silver {111}, {200} and {220}planes versus silver layer thickness for a zinc oxide metal-contact filmpart including second order polynomial fits to data, determined by usingregression analysis.

FIG. 8 is a plot of resistivity versus silver layer thickness for a zincstannate metal-contact film part and for a pair of zinc oxidemetal-contact film parts.

FIG. 9 is a table of Samples G-J showing film structures, depositionconditions, resistance and emissivity parameters.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Two Part Base Films

The base films of the present invention exhibit certain specialcharacteristics. They have, for instance, an atom arrangement conduciveto deposition of a low resistance, metallic, reflective film on top ofthem. Additionally, they exhibit chemical and heat stability.

According to the present invention, this desired combination ofcharacteristics is achieved by a base film having at least two parts, ametal-contact film-part having crystallization-directing properties, anda support film-part providing a stable foundation for the metal-contactfilm-part.

The coated articles of the present invention include a two-partantireflective base film formed on a substrate-near side of a metallic,reflective film. The metallic reflective film has two levels ofelectrical resistivity, one level being lower than the other. In thepractice of the invention, the lower of the two levels is preferred andis achieved by the two-part antireflective base film as discussed below.A first of the two film-parts, termed the "metal-contact film-part", isin contact with the metallic film. The material of this first part hascrystalline properties for causing the atoms forming the metallic filmto deposit in the lower of the two electrical resistivity levels. Thesecond of the two parts, termed the "support-part", supports the firstpart. The second part is chemically more durable than the first part,and is preferably an amorphous material, as compared to the first. Thepresent invention is applicable both for coatings having a singlemetallic, reflective film and for coatings with multiple metallic,reflective films, in which case a base film of the invention can beutilized for just one of the multiple metallic films, for several, orfor all of them.

The Metal-Contact Film-Part

The metal-contact film-part is chosen on the basis of an ability tocause the atoms of the metallic, reflective film to deposit in a formcharacterized by a low resistivity level. The metallic, reflective filmand the metal-contact film-part coordinate with one another, by which ismeant that a low resistivity level of the metallic, reflective film isassociated with a particular structural character of the metal-contactfilm-part. The crystal structure of the metallic, reflective film may,for instance, exhibit an orientation relationship with the metal-contactfilm-part. That, in turn, may result in larger grains, or alternativelyspeaking, smaller grain boundary area, or less of other electronscattering defects, within the film.

In general, the material chosen for the metal-contact film-part willdepend on the identity of the metallic, reflective film, whether themetallic, reflective film be, for example, gold, copper, or silver.

In the case where the metallic, reflective film is silver, an example ofa suitable material for the metal-contact part of the base film is zincoxide. In depositing the zinc oxide, care must be taken to selectprocess parameters that provide the zinc oxide with a suitablecrystallinity or preferential crystal growth orientation for favorablyaffecting deposition of the silver atoms. One way of doing this is tohave a preponderance of oxygen over argon during the sputtering of acast zinc metal target.

Another example of a suitable material for the metal-contact part of thebase film is zinc aluminum oxide sputtered from a ceramic tile ofappropriate composition. Still another example of a suitable materialfor the metal-contact part of the base film is indium tin oxide.

The Support Film Part

The support film-part, which may be divided into subparts, has at leastone part preferably in the form of a chemically and thermally resistant,preferably dielectric material. A suitable material is an amorphoussputtered oxide of zinc and tin, such as set forth in theabove-referenced U.S. Pat. No. 4,610,771, the disclosure of which isincorporated herein by reference.

It is also possible to deposit other dielectric films such as anamorphous oxide of tin or bismuth. For a high transmission and lowemissivity application, such dielectric films would be preferablynon-absorbing in the visible and infra-red portion of the spectrum.

As between the three, the oxide of zinc and tin (also referred to hereinas "zinc stannate", is preferred, because of its stronger bonding to thesubstrate and because of its greater chemical and thermal durability.

The Combined Metal-Contact Part and Support Film Part

In addition to being able to select base film-parts having the desiredcrystalline and amorphous properties described above, it is alsonecessary that they can be deposited with suitable thickness and indexof refraction. For instance, the base film-parts must adhere to theiradjoining materials with sufficient strength to withstand subsequenttransportation, manufacturing operations, and use, such as installationinto, and service in, multipane windows. Thickness and index ofrefraction affect the antireflection properties of the film, as is wellknown in the art.

The chemical durability of zinc stannate is superior to both zinc oxidesand tin oxides. This is substantiated in the work of F. H. Gillery. Aninvestigation of properties of zinc stannate is also reported by T.Minami et al. in "Properties of transparent zinc-stannate conductingfilms prepared by radio frequency magnetron sputtering", Journal ofVacuum Science and Technology A, Vol. 13, No. 3, (1995) pp. 1095-99.Therefore, because of zinc stannate's greater chemical durability, wherethe support film part of the base film is zinc stannate and themetal-contact film-part of the base film is zinc oxide, it is desirableto maximize the thickness of the zinc stannate layer for maximumchemical durability of the base film, and minimize the thickness of thezinc oxide layer, provided it remains of sufficient thickness to retainits ability to cause the metallic reflective film deposited on it toform its low resistance level, as explained above.

A preferred embodiment of the base film of the invention on a substrateis provided by the film-part sequence: substrate|oxide of zinc andtin|oxide of zinc, where: the oxide of zinc is the metal-contactfilm-part and the oxide of zinc and tin is the support film-part. Sinceonly atoms in the vicinity of the surface of the metal contact film havean effect on the depositing atoms of a metallic, reflective film, thethickness of the metal-contact film-part should, as a general rule, beminimized to that which is required to obtain the desired lowering ofthe electrical resistance of the metal film as explained above, so thatthe more chemically and thermally durable support film part may bemaximized. It is, however, understood that if the crystallinemetal-contact film-part is itself of sufficient durability, oralternatively, sufficiently protected by layers above it, e.g. by thefar-substrate anti-reflective layer or the protective overcoat that willbe described below, then the entire base coat, or a larger portion ofit, may be comprised of this material as will be demonstrated in Example3.

For example, the metal-contact film-part may have a minimum thickness inthe 20-30 Angstroms range, or below. On the other hand, greaterthickness in the support film-part helps that part to resist diffusionand chemical attack, so that the thickness of the support part should bemaximized. Total base film thickness is chosen to provide a suitableantireflection effect for the final appearance, e.g. color, of theproduct as is known in the art.

In addition to its favorable effect on the resistance of the reflectivemetal layer, the metal-contact film-part of the present invention wasfound to have a stabilizing influence on the structure of the reflectivemetal film during heat treatment that results in low haze. This will bedemonstrated by example below and by FIGS. 3, 4A, and 4B.

As noted above, the base film of the invention will be located, forinstance, between a transparent substrate and the first metallic,reflective film of the coating. If the coating contains more than onemetallic, reflective film, a plurality of the base films may be used,one for each of the metallic, reflective films of the coating.

The Substrate

While for some forms of the invention, such as temperable window pane,glass, for instance soda-lime glass, is clearly the material of choicefor the transparent substrate, nonmetallic substrates other than glass,such as various plastics, may be used.

The Metallic Reflective Film

As noted above, examples of suitable materials for forming the metallic,reflective films in articles of the present invention are gold, copper,and silver, with silver being preferred for most purposes, as is wellknown in the art. In general, a suitable metal is one which is a goodconductor of electricity, i.e. one having low electrical resistance,since that characteristic correlates well with ability to block escapeof heat from a heated house in the winter, or the influx of heat fromhot surroundings during the summer. Longer wavelength infrared radiationof the heat reaching a window having the metallic film in its coating isreflected back from whence it came. This ability is typically measuredin terms of the emissivity of the coated surface at room temperature(e.g. about 70° F. (21° C.)), with low emissivity being most desirable.Low emissivity may also be obtained by coatings that are notsignificantly reflective in the solar radiation range, e.g., in the nearinfrared.

The Primer Layer

On the substrate-far side of the metallic, reflective film, there willtypically be a primer film of an oxygen-capturing metal, such astitanium. The titanium acts as a sacrificial layer, to protect themetallic, reflective film during later deposition of an antireflectiveoxide film on the substrate-far side of the metallic, reflective film.Primer films may comprise other metals such as zirconium.

The optimal thickness of the titanium layer varies depending uponwhether the coated article of the present invention will be exposed toheat treatment during its production. Because the basic function of theprimer layer is to protect the metallic, reflective film from oxidizingduring the deposition of the antireflective oxide film on thesubstrate-far side of the metallic, reflective film, the primer layermay be thin where the coated article of the present invention will notreceive heat treatment during its production. "Thin" here refers toprimer film thicknesses on the order of 8 to 12 Angstroms. This is sobecause heat treatment is typically strongly oxidizing. In the absenceof heat treatment, the thin primer layer will suffice to protect themetallic, reflective film from oxidizing during production of the coatedarticle of the present invention. In an alternative embodiment of thepresent invention discussed in more detail below, the thin primer layermay be overcoated with a layer of zinc oxide to increase the shelf lifeof the coated article of the present invention.

However, if the coated article is to be heated during processing, athicker primer layer may be used, as taught in the above-referenced U.S.Pat. No. 4,806,220, the disclosure of which is incorporated herein byreference. As mentioned in that patent, if a single primer layer isdeposited over the reflective metal film, the primer thickness ispreferably greater than 20 Angstroms, up to 50 Angstroms in thickness.This thicker primer layer will withstand the strongly oxidizingconditions of heat treatment.

It has been found with the present invention, that here the coatedarticle will be exposed to heat treatment during its production, thereis a point at which the primer layer may be made either too thin or toothick. Too thin a primer layer results in a lack of protection for thereflective, metallic film from oxidation at high temperature thusrendering the coated article unacceptable for heat treatment and in poorshear resistance which makes the article unsuitable for long distanceshipment for later thermal processing. Too thick a primer layer, resultsin the formation of an undesirable haze in the coated article after heattreatment, also rendering it unacceptable for heat treatment.

The optimum range of titanium thickness that provides sufficientprotection without forming undesirable haze is demonstrated in FIG. 3.Especially in conjunction with a zinc oxide metal-contact film-part, ithas been found that the preferred subrange of the thickness of theprimer layer that will provide a coated article suitable for heattreatment during its manufacture, is where the primer layer is in thevicinity of 20 Angstroms in thickness. Below that range the coating mayhave poor shear resistance and above that range the coating may develophaze to an unacceptable level after heat treatment. In the case oftitanium metal primer, an empirically determined coating thicknessgiving adequate shear strength and acceptably low haze is in the rangeof from about 22 Angstroms to about 30 Angstroms. A preferred range isfrom about 24 Angstroms on the lower side to about 28 Angstroms on theupper side.

The Antireflective Film

The antireflective film on the substrate-far side of the metallic,reflective film is selected on the basis of index of refraction,adherence, and chemical durability, similarly as above. An example of asuitable material is oxide of zinc and tin. In the case of a coatinghaving two metallic, reflective films, the antireflective film on thesubstrate-far side of the first metallic, reflective film can serve as abase film of the invention for the second metallic, reflective film.

The Protective Overcoat

Typically, a coating of the invention will be capped by an exterior,protective overcoat, such as a hard layer of titanium oxide. Such istaught by F. H. Gillery et al. in U.S. Pat. No. 4,716,086, thedisclosure of which is incorporated herein by reference.

Layer Stack Arrangements of the Present Invention

Single Stack Suitable for Heat Treatment

In one embodiment of the present invention, there is provided a hightransmittance, low emissivity coated article suitable for heat treatmenthaving a single metallic, reflective layer, also known as a singlestack, which includes:

a transparent, nonmetallic substrate;

a dielectric, antireflective base film deposited on the substrate, thebase film including a crystalline metal-contacting film-part and asupport film-part where the support film-part is in contact with thesubstrate and where the support film-part is comprised of a materialother than the crystalline metal-contacting film-part;

a metallic reflective film deposited on the crystalline metal-contactingfilm-part of the base film;

a primer film deposited on the metallic reflective film; and

a dielectric, antireflective film deposited on the primer film.

In an alternative embodiment of the present invention, an exteriorprotective overcoat layer deposited on the dielectric antireflectivefilm.

In a preferred embodiment of the present invention, the transparent,nonmetallic substrate is glass, the support film-part is a zinc stannatefilm, the crystalline metal-contacting film-part is a zinc oxide film;the metallic reflective film is a silver film, the primer film isdeposited as titanium metal, the dielectric, antireflective film is azinc stannate film, and the exterior protective overcoat layer is atitanium oxide film.

Double Stack Suitable for Heat Treatment

In an alternative embodiment of the present invention there is provideda high transmittance, low emissivity coated article suitable for heattreatment having two metallic, reflective films, also known as a doublestack, which includes:

a transparent, nonmetallic substrate;

a first dielectric, antireflective base film deposited on the substrate,the base film including a crystalline metal-contacting film-part and asupport film-part where the support film-part is in contact with thesubstrate and where the support film-part is comprised of a materialother than the crystalline metal-contacting film-part;

a first metallic reflective film deposited on the crystallinemetal-contacting film-part of the base film;

a first primer film deposited on the metallic reflective film;

a second dielectric, antireflective base film deposited on the primerfilm, the second dielectric antireflective base film including acrystalline metal-contacting film-part and a support film-part where thesupport film-part is in contact with the primer film and where thesupport film-part is comprised of a material other than the crystallinemetal-contacting film-part of the second base film;

a second metallic reflective film deposited on the crystallinemetal-contacting film-part of the second base film;

a second primer film deposited on the second metallic reflective film;and

a dielectric, antireflective film deposited on the second primer film.

In a preferred embodiment of the above described embodiment of thepresent invention, an exterior protective overcoat layer is deposited onthe dielectric, antireflective film.

In a preferred embodiment of the above described alternative embodimentof the present invention, the transparent, nonmetallic substrate isglass, the support film-part of the first base film is a zinc stannatefilm, the crystalline metal-contacting film-part of the first base filmis a zinc oxide film; the first metallic reflective film is a silverfilm, the first primer film is deposited as titanium metal, the supportfilm-part of the second base film is a zinc stannate film, thecrystalline metal-contacting film-part of the second base film is a zincoxide film; the second metallic reflective film is a silver film, thesecond primer film is deposited as titanium metal, the dielectric,antireflective film is a zinc stannate film, and the exterior protectiveovercoat layer is a titanium oxide film.

Non-temperable Double Stack

In still another embodiment of the present invention, where the hightransmittance, low emissivity coated article is a double stack includingtwo reflective metallic films, and where it is not intended to besubjected to heat treatment during its manufacture, an article withimproved shelf life may be obtained as follows. The article is formed bydepositing the above described two part base film between the substrateand the first metallic, reflective film, and depositing a three partbase film interposed between the two metallic, reflective films, and byinterposing an additional zinc oxide layer as part of the dielectricantireflective film, between the second primer film and the zincstannate dielectric antireflective film. In this embodiment, the coatedarticle includes:

a transparent, nonmetallic substrate;

a first dielectric, antireflective base film deposited on the substrate,the base film including a crystalline metal-contacting film-part and asupport film-part where the support film-part is in contact with thesubstrate and where the support film-part is comprised of a materialother than the crystalline metal-contacting film-part;

a first metallic reflective film deposited on the crystallinemetal-contacting film-part of the base film;

a first primer film deposited on the metallic reflective film;

a second deposited on the primitive base film deposited on the primerfilm, the second dielectric antireflective base film including acrystalline metal-contacting film-part which is a zinc oxide film, and asupport film-part, wherein the support film-part is further comprised ofa first layer of a zinc oxide film in contact with the first primer filmand a second layer of a zinc stannate film in contact with thecrystalline metal-contacting film part;

a second metallic reflective film deposited on the crystallinemetal-contacting film-part of the second base film;

a second primer film deposited on the second metallic reflective film;and

a dielectric, antireflective film deposited on the second primer filmwherein the dielectric, antireflective film includes a first layer of azinc oxide film deposited on the primer film and a second layer of azinc stannate film deposited on the first zinc oxide layer of thedielectric, antireflective film.

In an alternative embodiment of the above described embodiment of thepresent invention, an exterior protective overcoat layer is deposited onthe dielectric antireflective film.

In a preferred embodiment of the above described alternative embodimentof the present invention, the transparent, nonmetallic substrate isglass, the support film-part of the first base film is a zinc stannatefilm, the crystalline metal-contacting film-part of the first base filmis a zinc oxide film; the first metallic reflective film is a silverfilm, the first primer film is deposited as titanium metal, the secondmetallic reflective film is a silver film, the second primer film isdeposited as titanium metal, and the exterior protective overcoat layeris a titanium oxide film.

In the above described embodiments, the zinc oxidelzinc stannate portionof the three part base film forms the support film-part, and the zincoxide film forms the metal-contact film-part.

The primer layer of this embodiment may be thinner than the embodimentssubjected to heat treatment, on the order of 8-12 Angstroms, for thereasons set forth above.

The additional zinc oxide film of the dielectric antireflective film ofthe above described embodiment provides extended shelf life of thecoated article of the present invention.

Manufacturing and Physical Characteristics of Heat Treatable andNon-Heat Treatable Articles

Typically a window manufacturer utilizes window panes received from aglass pane manufacturer, which the window manufacturer incorporates intofinished window products.

Certain window applications require tempered glass. Glass tempering isachieved by heating the article to a certain temperature followed byquenching of the heated article. Tempered glass is typically strongerthan annealed glass. Further, tempered glass windows shatter into smallpieces when impacted with sufficient force to break them, as opposed tonon-tempered glass which will shatter in larger shards of glass.

One limitation of tempered glass is that it cannot be cut to size.Therefore, in one method of producing tempered glass windows, the panemanufacturer ships standard, cuttable sizes of annealed, temperable,pane to the window manufacturer. The window manufacturer cuts blanksfrom the larger standard sizes for the windows for which it has ordersand then tempers the blanks so cut.

An alternative way of manufacturing tempered glass windows, is that thepane manufacturer, not the window manufacturer, does the tempering,either of temperable, coated pane, or of uncoated pane, followed bycoating. However, in either case, this introduces the complication forthe pane manufacturer of maintaining a wide variety of non-standardsizes in the pane manufacturer's operations and inventory or forsubstantial lead time for the pane manufacturer to make the panes andthen ship them to the window manufacturer.

Where the glass is coated, heating in the tempering range anneals thecoating layers and further stabilizes the thin film stack. Most notably,the resistivity of the silver layer(s) decreases and the titanium primerlayer oxidizes and becomes more transparent in the visible range of thespectrum. On the other hand, also as a result of heating, sodium orother impurities can diffuse through the layers of the coating andoverheating of the coated glass or, alternatively, extended exposure tohigh temperature may result in breakdown of the coating (as, forexample, by agglomeration of silver into particles) and excessive haze.

As compared to uncoated clear glass, it is more difficult to increasethe temperature of coated low-emissivity glass. The metallic, reflectivemetal film in low-emissivity glass effectively reflects much of theenergy radiated from the heat source in a furnace. Therefore, thetemperature of the heating element, its duty cycle, the line speed(residence time in the furnace), or all of the above have to be adjustedin order to achieve the desired final temperature in the coated glass. Alehr based on forced convection heat transfer may be advantageous inthis respect.

Preferably, tempering is carried out in a lehr that can rapidly elevatethe glass temperature to within the required range (1160° F. (627° C.)to 1250° F. (677° C.), preferably 1170° F. (632° C.) to 1200° F. (649°C.)). Rapid elevation of the temperature minimizes the high temperatureexposure time and, as a result, the coating will obtain and retain itsoptimum properties. A high line speed, or short cycle time, can also beadvantageous from a manufacturing point of view.

The lehr may be electric or a gas hearth. The lehr may be continuous,where glass travels at a constant speed through the furnace, or of abatch type, where glass enters the furnace and is held stationary, or isoscillated, for a given time. Upon leaving the lehr, the glass isimmediately air quenched, in order to impart the temper.

Further illustrative of the invention are the following examples:

EXAMPLE 1 Heat Treatable Single Stack

A multiple layer coating which was comprised of: zinc stannate film|zincoxide film|silver|titanium|zinc stannate|titanium dioxide was depositedon a substrate as follows, with the purpose of providing a coated glasspane which can be subsequently tempered. The substrate was a 3.3 mm(0.13 inch) thick pane of clear, annealed, soda-lime glass.

The coating of this example was deposited in a multi-chamber, in-line,magnetron sputtering, 84-inch (213 cm) coater, as manufactured by AircoCoating Technology of Fairfield, Calif. Different chambers in the coaterwere dedicated to the deposition of either metal or dielectric (oxide)layers and the glass moved at constant speed under cast metal cathodetargets that were energized at all times. The gas composition in theoxide chambers was set at 80% oxygen-20% argon at a total pressure of 4mTorr. Pure argon at a pressure of 5 mTorr was used in the metaldeposition chambers.

The coating was formed by first depositing a two part antireflectivedielectric base film (thickness of 318±4 Angstroms) consisting of afirst support-part of a 257±13 Angstroms thick film of amorphous zincstannate contiguous to the glass substrate and a second metal-contactfilm-part of a 58±7 Angstrom thick crystalline zinc oxide film depositedon the zinc stannate film. The zinc oxide film was multigrained, ratherthan single crystal. The thicknesses were measured by a stylus profiler.Due to the proximity of their optical indices, the above two partstogether act as a single optical film with a transmittance ofapproximately 82%.

While in bulk form, the formula for zinc stannate is Zn₂ SnO₄, itssputtered composition may vary as Zn_(x) SnO_(y). Although the XRFmethod was described above as the preferred method to measure thethickness of metallic films, it can also be used in connection withdielectric films to determine the composition of the dielectric films asopposed to the thickness of such dielectric films. The composition ofthe zinc stannate film was determined by the XRF method as follows. Theμg/cm² of the zinc and tin metals of the zinc stannate film was measuredwith the XRF method. Then, by assuming that the oxides arestoichiometric with their metal counterparts, i.e. Zn=ZnO and Sn=SnO₂,this led to a composition which may alternatively be expressed as: Zn:Snweight ratio of 0.93±0.12; Zn:Sn atom ratio of 1.7±0.2; or compoundformula of approximately Zn₁.7x Sn_(x) O₃.7x.

Upon moving the substrate from the oxide deposition chambers to themetal deposition chamber, an approximately 115 Angstrom thick film ofmultigrained silver was deposited onto the crystalline zinc oxide upperpart of the base film. The measured thickness of the base film plussilver film totaled 434±9 Angstroms and the transmittance of the coatedglass, as measured by an in-line transmission monitor, was reduced to63.5% due to the reflective silver film. The thickness of the silverfilm corresponds to approximately 10.0 μg of this metal per cm², asmeasured by x-ray fluorescence.

Next, a sacrificial titanium primer film with a thickness equivalent to1.1 μ/cm² (corresponding to a thickness of about 24 Angstroms) wasdeposited on the top of the silver.

The deposition of the titanium primer film was followed by deposition ofan antireflecting topcoat film of zinc stannate with a thickness of230±7 Angstroms and a final titanium dioxide overcoat with a thicknessof 36±6 Angstroms.

The above multilayer coating passed a shear resistance test (describedin the following paragraph) by receiving a rating of 60. It had a sheetresistance of 7.1 Ω/sq. (to convert sheet resistance in Ω/sq. toresistivity in μohm.cm, multiply values in Ω/sq. by silver filmthickness in centimeters (1 Angstrom=10⁻⁸ cm) and divide by 10⁻⁶) and anemissivity of ε=0.12. The emissivities of coatings described herein weremeasured with a model AE Emissometer manufactured by Devices andServices Co. of Dallas, Tex. Measurements according to ASTM E 1585-93using a Mattson Galaxi Model 5200 FTIR instrument with CsI opticsgenerally yielded emissivity values of up to 20% less within the rangeof interest here. The visible light transmission of this sample wasequivalent to 76% (VLT(D65), where D65 is reference to a standardilluminant) and its visible reflection was equivalent to Y(D65)=5.66% onits coated side. The coated side CIE 2° observer color coordinates ofthis sample were x=0.3350 and y=0.3239.

The shear resistance test consists of applying 20 successive strokes ofa cloth wetted with deionized water against the coated surface of glass,followed by visual examination of the tested area. Depending on theappearance of the tested area, letter grades of D-, D, D+, . . . , A, A+are assigned to the coating; then, for numerical analysis, assignmentsof 5 to D-, 10 to D, . . . 55 to A, and 60 to A+ are made. If a coatingshows no signs of shear, not even barely visible scratches, then itreceives a maximum rating of 60. Coatings that display uniform shear anddelamination at any interface of the multi-layer coating within the testarea receive a failing rating of zero. Other levels of performancereceive intermediate scores. This method of coating durabilitycharacterization has been found to correlate well with field performanceof the coating.

A 2 inch×8 inch (5.08 centimeter×20.32 centimeter) section of the abovesample was heated to a maximum temperature of 1184° F. (640° C.) tosimulate the thermal cycle of the tempering process. This resulted in acoating that retained a rating of 60 in the shear test (the coating getseven harder after tempering), and had no measurable haze, as measuredwith a haze meter (HAZEGARD Model No. XL-211, a product of PacificScientific Company, Silver Spring, Md.) and a very low level of coatinghaze when viewed using a dark room, flood-light haze test, as describedin the following paragraph. The resistance and emissivity of the heatedsample improved to 4.5 Ω/sq. and 0.07, respectively, while its visiblelight transmission increased to 88.0%. The reflected color coordinatesof the coated side of the sample shifted to a neutral color ofY(D65)=5.2, x=0.2812 and y=0.2860 after heat.

In the dark room, floodlight haze test, the coated specimen is viewed inreflection in a dark room at various viewing angles relative to aspotlight, in order to find the geometry yielding maximum scattering oflight, or, in other words, haze, possible from the coating. If there isno geometry that can make haze observable, an A+ rating is assigned tothe sample. Very poor samples receive D-. For purposes of numericalanalysis, the letter grades are given values of 5 to 60, as describedabove for the shear test. Lower haze corresponds to higher numericalvalues.

The particular film, or layer, thicknesses used in this exampleinfluence the color and emissivity of the final product. But, choice ofthickness is also influenced by manufacturing issues. The thicknesses ofthe dielectric layers and silver can be modified to obtain a largepallet of colors. Thickness of the titanium primer is limited by itseffect on protection of the silver layer during the deposition process,on coating hardness (shear resistance) and on haze, as will becomeapparent in the EXAMPLES ON EFFECT OF PRIMER THICKNESS, as set forthbelow. The thickness of the titanium dioxide overcoat should exceed aminimum, in order to impart the desired chemical durability to thestack, but is limited on the upper side by its low rate of depositionand manufacturing economics.

While this EXAMPLE uses only one layer of silver, it is understood thatits principles can be built upon to provide a heatable glass coatingwith multiple silver films. An example of this is a coated article ofthe following sequence: glass sheet substrate|oxide of zinc-tinalloy|oxide of zinc|silver|titanium|oxide of zinc-tin alloy|oxide ofzinc|silver|titanium|oxide of zinc-tin alloy|an exterior protective filmof oxide of titanium.

EXAMPLE 2

Large plates of coated glass similar to that of EXAMPLE 1 weresuccessfully shipped to a tempering plant in another state, using thesame packaging and shipping methods used for other low-emissivity coatedglass products, and tempered on a continuous electric tempering line. Atthe tempering plant, the glass was cut to size, seamed with an automaticseamer, washed in a flat glass washer using deionized water, and driedwith clean compressed air. "Seaming" is a sanding of the edges of glassto remove microcracks which would propagate during the temperingprocess. The glass then traveled through the lehr of the line atconstant speed and was air quenched upon exiting the lehr. The glass wassubsequently washed a second time in preparation for installation in aninsulated glass window unit. The properties of the coated glass afterthe above treatment were comparable to those listed in EXAMPLE 1 for theheated coated glass specimen. The coating was durable enough for theinterstate shipping and for the cutting, seaming and washing stepsbefore the tempering process.

EXAMPLES ON EFFECT OF PRIMER THICKNESS

A series of samples were prepared and tested experimentally to determinethe effect of the thickness of the titanium primer film on shearresistance, visible light transmission (VLT), and sheet electricalresistance. The samples were prepared in the same manner as the sampleof EXAMPLE 1 described above, with the following exceptions. First, thesilver layer thickness was set at 90 Angstroms (calculated from themeasured 9.5 μg/cm²) as opposed to the 115 Angstrom thick layer ofEXAMPLE 1. Second, while all samples received a zinc stannate film onthe substrate, only a portion of the samples received a zinc oxide filmover the zinc stannate film before deposition of the silver layer, thuscreating a set of zinc stannate metal-contact film-part samples and aset of zinc oxide metal-contact film-part samples. The titanium primerlayer thickness was then varied for each of these two sets and theremaining layers were deposited as described in EXAMPLE 1. The testparameters were otherwise as set forth in EXAMPLE 1.

FIGS. 1A and 2A are plots of the effect of variations in titaniumthickness on the shear resistance, visible light transmission andelectrical resistance of the amorphous zinc stannate metal-contactfilm-part samples. FIGS. 1B and 2B give results of the same tests, butwhere the crystalline zinc oxide metal-contact film-part samples wereused. Data for visible light transmission and electrical resistance aregiven for both before and after heating to tempering temperature for allsamples.

It was found that, shear resistance increases after heating to temperingtemperature, but this is not shown in the figures. All of FIGS. 1Athrough 2B show that shear resistance, also referred to as coatinghardness, passes through a minimum at titanium primer thicknesses ofabout 17 Angstroms.

Transmission increases after heating to tempering temperature, due tooxidation of the primer film and perhaps due to annealing of thereflective metal film, silver.

The beneficial effect of the zinc oxide on electrical resistance,particularly after tempering in the case of the thicker titanium films,is evident by the lower resistance values obtained.

The after-heat samples of both the zinc oxide metal contact film partsand the zinc stannate film parts were tested for haze. FIG. 3 shows theresults of the haze rating testing, as determined by the dark room,floodlight haze test. The samples with the zinc oxide metal-contactfilm-part go through a pronounced peak of desirable high haze ratingcorresponding to low haze, at about 24 to 28 Angstroms of thickness ofthe titanium primer layer as shown in FIG. 3.

EXAMPLES ON EFFECT OF METAL-CONTACT FILM-PART THICKNESS

The discovery of the effect of titanium primer film thickness on hazewas supplemented with a series of examples wherein samples A through Fwere prepared where the thickness of a zinc oxide metal-contactfilm-part over a zinc stannate support film part was varied from 0Angstroms to 68 Angstroms in thickness while the titanium primerthickness was held constant at 28 Angstroms. The samples and testparameters were otherwise as set forth in EXAMPLE 1. The samples weretested for haze, and the data are presented in Table 1, where thethickness of the zinc oxide metal contact film part is correlated withthe after-heat haze rating.

                  TABLE 1                                                         ______________________________________                                        ZINC OXIDE THICKNESS (Å)                                                                            HAZE RATING                                         ______________________________________                                        Sample A      68          A+     (60)                                         Sample B      56          A      (55)                                         Sample C      45          A      (55)                                         Sample D      22          A      (55)                                         Sample E       0          D-      (5)                                         Sample F      56          A-     (50)                                         ______________________________________                                    

These tabulated results agree with the data of FIG. 3 in that the lowesthaze rating (and therefore worst haze) corresponds to the Sample E whereno zinc oxide was deposited resulting in a zinc stannate metal-contactfilm-part. The other Samples A through D and F show consistently highhaze ratings (low haze levels), which appear from the data in Table 1 tobe independent of zinc oxide thickness.

The effect of thickness of the metal-contact film-part on planar indiceswas tested with Samples E and F of Table 1 by obtaining diffractionspectra of the Samples. FIGS. 4A and 4B correspond to the before-heatand after-heat, diffraction spectra of the Samples E and F of Table 1,respectively.

The x-ray diffraction method used for the spectra presented herein isthe grazing-angle method. In this configuration, the x-ray source isdirected towards the sample at a fixed, small angle (≦1.0 degrees), inorder to maximize the signal from the thin film coating. The x-raydetector is swept in a vertical plane normal to the sample surface, inorder to measure the intensities of the diffracted x-ray peaks. Thesample angle relative to the source is kept constant, but the samplerotates in its own plane about its surface normal. For furtherinformation on this technique, see T. C. Huang, in "Advances in X-RayAnalysis", Vol. 35, Ed. C. S. Barnett et al., Plenum Press, New York,1992, p 143.

For a multigrained, or polycrystalline, film with a random orientation,the diffraction pattern, or spectrum, of silver is similar to that of apowder sample, where the {111} peak is most prominent. Table 2 shows thediffraction pattern for silver powder, as taken from the JCPDS-ICDDPowder Diffraction Database.

                  TABLE 2                                                         ______________________________________                                        JCPDS-ICCD Powder Diffraction Data for Silver                                 Silver Plane*  2-Theta Relative Intensity                                     ______________________________________                                        111            38.117  100                                                    200            44.279  40                                                     220            64.428  25                                                     311            77.475  26                                                     222            81.539  12                                                     ______________________________________                                         *Only Planes up to 2θ value of 85 degrees are shown here.          

While the pre-heat, or before heat, spectrum in FIG. 4B corresponds toSample F, it is also typical of those of the diffraction spectra ofSamples A through D as well, but differs considerably from that of FIG.4A. Comparing pre-heat 4B to pre-heat 4A, the presence of the zinc oxidemetal-contact film-part in FIG. 4B reduces the intensity of the peak forthe silver close-packed {111} planes but promotes the peak for the {220}planes. Planes, like the {220} planes, which do not have close packing,are referred to herein as "less packed" planes.

The rise of the {220} peak above the {111} peak in to FIG. 4B comparedto FIG. 4A is indicative that the thin silver film of FIG. 4B has apreferential crystallographic orientation relative to the substrate, ascompared to the more random distribution of grain orientations in FIG.4A resembling the spectrum which would be obtained from a powder sample.This, however, does not suggest that the {220} planes are parallel tothe substrate. In fact, due to the asymmetric x-ray diffraction geometrydescribed above, the {220} planes are at an angle relative to the planeof the substrate.

Comparing the post-heat, or after heat, spectra, it will be noted thatthe sample of FIG. 4B with the zinc oxide metal-contact film-partcontinues to show a {220} peak, while exhibiting essentially no {111}peak. Thus, the preferential orientation of the pre-heat zinc oxidesample has been retained even after heating. In the sample of FIG. 4A,without a zinc oxide metal-contact film-part, while a {220} peak hasdeveloped after heating, the {111} peak towers above it, indicatingretention of an essentially random grain orientation.

The shapes of these spectra are specific to the diffraction geometrydescribed above. Other diffraction geometries will yield spectra, whichwhile different in appearance, still indicate preferred grainorientation for the zinc oxide samples.

EXAMPLES ON EFFECT OF TWO VARIABLES

A two-variable designed experiment was conducted to show the effect ofvarying thicknesses of a zinc oxide metal-contact film-part and atitanium primer film on coating resistance before and after heattreatment. A set of 22 samples were prepared as set forth in EXAMPLE 1,except that the zinc oxide metal-contact film parts and titanium primerlayer thicknesses were varied to provide a randomized set of trials fora designed experiment. All other experimental conditions were as setforth in EXAMPLE 1, except silver film thickness which was held constantat 9.95±0.22 μg/cm² =95±2 Angstroms (based on density calculations) asopposed to the 115 Angstrom thick silver layer of EXAMPLE 1. Theexperimental results were processed in a commercially-availablestatistical computer program to provide the plotted surfaces of FIGS. 5Aand 5B.

EXAMPLES ON EFFECT OF THE COMPOSITION OF THE METAL-CONTACT FILM-PART ANDDEPOSITION OXYGEN CONCENTRATION ON PLANAR INDICES FORMATION, RESISTANCEAND EMISSIVITY

Four samples were prepared and tested to demonstrate the effects of: 1)oxygen concentration during deposition of a zinc oxide metal-contactfilm-part; and 2) to demonstrate the effect of the composition of themetal-contact film-part--specifically whether it was comprised ofcrystalline zinc oxide with strong preferred orientation, crystallinezinc oxide without strong preferred orientation, or whether it wascomprised of amorphous zinc stannate. The Samples G through J wereprepared as set forth in FIG. 9. Cast metal cathode targets were used.Grazing-angle diffraction spectra for Samples G through J are presentedin FIGS. 6A-6D respectively. The spectra are for the coatings of FIG. 9before any heating such as for tempering. Resistivity and emissivitywere also measured and are set forth in FIG. 9. It is to be noted thatFIG. 9 provides a direct comparison of multilayered films includingsubstrate|zinc oxide|silver formulation (Samples G, H and J) with amultilayered film including substrate|zinc stannate|silver formulation(Sample I) to provide direct comparisons of the metal-contact film-partswithout the use of a separate support-part film. It is also to be notedthat Sample J is corroborative of Sample H, being prepared undervirtually identical circumstances.

Samples H and J show a low level of electrical film resistance, whileSamples G and I show a high electrical film resistance, corresponding tothe silver having two different electrical resistance levels. Samples Hand J show low resistance and correspond to zinc oxide deposition at ahigher, 80% oxygen concentration, and the spectra for these samples areshown in FIGS. 6B and 6D.

At the outset, the results shown in FIG. 9 show that where the metalcontact film-part is amorphous zinc stannate, as in Sample I, electricalresistance is clearly higher than in Samples H and J. The inventors havefound that varying the oxygen-content of the atmosphere duringdeposition of the zinc stannate metal-contact film-part has no effect onlowering the resistivity, as the metal-contact film-part has nocrystalline-forming or crystalline-directing properties. Thus, neitherthe composition (zinc stannate) of the metal-contact film part, norvariations in the oxygen concentration during its deposition provide thedesired results of the present invention.

In contrast, Samples H and J show significantly lower resistance where azinc oxide metal-contact film-part is used. These two samples correspondto an oxygen concentration of 80% during the deposition of the zincoxide metal contact film part. The inventors have also found thatvarying the oxygen concentration during deposition of the zinc-oxidemetal-contact film-part significantly impacts resistance thusdemonstrating that silver has two different electrical resistance levelsand that a choice of the levels can be obtained by controlling oxygenconcentration during deposition of the metal-contact film-part. Theforegoing is shown by a comparison of Sample G (zinc oxide metal-contactfilm-part, 50% O₂ /50% argon, resistance 3.52 ohms/sq.) versus Samples Hand J, (zinc oxide metal contact film part, 80%O₂ -20%Ar, resistance2.92 and 2.85 ohms/sq. respectively). Thus both the composition of themetal-contact film-part (zinc oxide versus zinc stannate) and its oxygenconcentration during deposition have a significant impact on theresistance of the multilayered films formed.

Tests of the diffractions spectra of Samples G through J confirm thatthe peaks of the silver {220} planes are higher than the {111} planesfor Samples H and J than for Samples G and I. As compared to thepatterns of FIGS. 6A (Sample G) and 6C (Sample I), the peaks in FIGS. 6B(Sample H) and 6D (Sample J) for the {220} silver planes are higher thanthose for the {111} planes. As compared to the pattern of FIG. 6A, thepeaks for the {103} zinc oxide planes in FIGS. 6B and 6D are higher thanin FIG. 6A. It appears that a zinc oxide metal-contact film-partdeposited at the higher, 80% oxygen concentration has a differentcrystalline character which causes the grains of the subsequentlydeposited silver films to orient preferentially in the form having thelower electrical resistance level.

The rise of the {103} peak of zinc oxide over its other lower indexpeaks in FIGS. 6B and 6D is in contrast to the powder diffractionpattern of zinc oxide, as shown in Table 3 below. This behavior issimilar to the case for silver, as described above, and indicates apreferential growth of the zinc oxide film with the {103} planes at aninclination relative to the plane of the substrate. This preferentialorientation of the zinc oxide film causes the preferential growth ofsilver above it, which, in turn, results in better electricalconductivity within the metallic film. These observations have beensupported by high resolution transmission electron microscopy analyses.

As discussed above, the shapes of these spectra are specific to theparticular diffraction geometry used in these experiments.

                  TABLE 3                                                         ______________________________________                                        JCPDS-ICDD Powder Diffraction Data for Zinc Oxide                             Zincite Plane* 2-Theta Relative Intensity                                     ______________________________________                                        100            31.770  57                                                     002            34.442  44                                                     101            36.253  100                                                    102            47.539  23                                                     110            56.603  32                                                     103            62.864  29                                                     200            66.380   4                                                     112            67.963  23                                                     201            69.100  11                                                     004            72.562   2                                                     202            76.995   4                                                     104            81.370   1                                                     ______________________________________                                         *Only Planes up to a 2θ value of 85degrees are shown here.         

FURTHER EXAMPLES USING X-RAY SPECTRA

A series of samples were prepared and tested to demonstrate further thereversal of the intensities of the silver {111} and {220} planes for azinc oxide metal-contact film-part of the invention compared to anamorphous zinc stannate metal contact film-part for silver layers ofvarying thickness. These comparisons were conducted without the use of aseparate support film part as explained above. The zinc oxide metalcontact film part samples were prepared by depositing zinc oxide on thesubstrate in a 20%-80% argon-oxygen atmosphere, which as noted above,results in the preferential growth of {220} planes of silver. The zincstannate metal contact film part samples were prepared by depositingzinc stannate on a substrate in a 65%O₂ /35Ar atmosphere which as notedabove results in no preferential growth of {220} planes of silver. Bothsets of examples were then coated with silver layers of varyingthickness, and peak intensities were determined via x-ray diffraction.The results are shown in FIGS. 7A and 7B. Using regression analysis, asecond order polynomial was fitted to the data, and these correspondingcurves are also shown in FIGS. 7A and 7B. The results shown in FIGS. 7Aand 7B demonstrate that in samples lacking the zinc oxide metal-contactfilm-part (FIG. 7A), the silver {111} planes dominate the diffractionspectrum, while, with the zinc oxide metal-contact film-part present(FIG. 7B), the {220} planes become the primary peak. This behaviorcontinues up to silver film thicknesses of 500 Angstroms, or more. Thatis, the structure of the initial nucleation layer of silver has apronounced effect on the growth of the silver film as it develops into asignificantly thicker layer.

EXAMPLES ON RESISTIVITY VERSUS SILVER THICKNESS

A series of samples were prepared and tested to show that themetal-contact film-part of the present invention places silver in alower resistance form at silver film thicknesses of interest for hightransmittance, low emissivity coated glasses. The samples were preparedin the same manner and in the same deposition atmospheres as the samplesof FIGS. 7A and 7B to provide a set of zinc oxide metal-contactfilm-part samples and a set of zinc stannate metal-contact film-partsamples, with the exception that the zinc oxide metal-contact film-partsamples were subdivided into a first subset prepared with a 1.5 inch(3.8 cm) cathode-to-substrate spacing and a second subset with a 5.5inch (13.97 cm) cathode-to-surface spacing to also test whether suchspacing affected resistivity. All samples were then overcoated withsilver layers of varying thickness and resistance was measured.

The results are shown in FIG. 8, expressed in terms of film resistivityversus silver thickness.

Resistivity of bulk materials is independent of the sample size. Forthese samples with the thin silver films, however, film resistivity isquite high until the thickness exceeds 50 Angstroms, or more. At lowerthicknesses, the film is discontinuous and in the form of isolatedislands or of a very rough morphology and, thus, resistance is high. Allcurves fall as silver thickness increases and appear to approach a thickfilm resistivity value. This is due to the increasing effect of the bulkproperties of the silver. With the present invention, the resistivitycurves for both of the zinc oxide metal contact film part samples areshifted to a lower level than the curve for the zinc stannatemetal-contact film-part samples. The largest differences correspond to asilver thickness of 80-200 Angstroms, which is most significant to thefield of high transmission, low emissivity coatings.

EXAMPLE 3 Untempered Double Stack

A multiple layer coating was deposited on a substrate in the form of a2.5 mm (0.098 inch) thick pane of clear, annealed, soda-lime glass. Thecoater, and its operation, have already been described in EXAMPLE 1. Thecoating in this Example was formed by first depositing a 320 Angstromdielectric base film consisting of a support film-part of amorphous zincstannate contiguous to the glass substrate and a metal-contact film-partof crystalline zinc oxide layer on the zinc stannate. The relativethicknesses of the two film-parts of this base film were as in EXAMPLE1.

Next, a layer of silver film was deposited on the crystalline zincoxide. The thickness of the silver film was equivalent to 9.5 μg/cm² ofsilver (XRF), which corresponds to approximately 90 Angstroms of a filmwith silver's bulk density.

Next, a sacrificial titanium primer film with a thickness equivalent to0.4 μg/cm² (corresponding to a thickness of about 9 Angstroms of a filmwith the bulk density of titanium) was deposited on the top of thesilver.

The deposition of these metal films was followed by deposition of anapproximately 805 Angstroms three part antireflecting dielectric basefilm. This three part base film consisted of a zinc oxide|zincstannate|zinc oxide film-part sequence with an approximate 26%/35%/39%thickness ratio. Here, the zinc oxide|zinc stannate sequence is thesupport film-part, and the top zinc oxide, representing 39% of thethickness, is the metal-contact film-part destined to receive a secondsilver film of the coating as described below.

It is to be noted that the zinc oxide film is thicker in themetal-contact film-part (39%) than the zinc oxide film in the supportfilm-part (26%) in this example, due only to manufacturing limitationsof the equipment used to deposit the films. The resulting coating wasstill sufficiently chemically, though not thermally, durable. However,as noted above, it remains advantageous to minimize the thickness of thezinc oxide film in the metal-contact film-part, provided it can stillcause the low resistive reflective metal film to form as describedabove.

A second reflective film of silver was then deposited on the top of thedielectric composite film. This second layer had an equivalent thicknessof 130 Angstroms as derived from a measured value of 13.4 μg/cm² ofsilver in a separate experiment.

A sacrificial titanium primer layer with a thickness equivalent to 0.45μg/cm² (corresponding to a thickness of about 10 Angstroms of a filmwith the bulk density of titanium) was deposited on the top of thesecond silver film.

Next, a 270 Angstrom antireflective film, consisting of a first zincoxide film-part deposited over the primer layer and a second zincstannate film part deposited over the first zinc oxide film part with a40%/60% thickness ratio was deposited.

This antireflective layer was followed by a final, approximately 30Angstrom thick, titanium dioxide overcoat.

The coating of this EXAMPLE 3 passed the shear resistance test byreceiving a rating of 60. It had a sheet resistance of 2.23 Ω/sq. and anemissivity of 0.05, or lower.

The visible transmittance of this sample was 81.6% and its visiblereflectance was equivalent to Y(D65)=4.75 on its coated side. The coatedside CIE 2° observer color coordinates of this sample were x=0.3088 andy=0.3461.

As in EXAMPLE 1, the choice of the above silver and dielectric layerthicknesses is based on the desired color and emissivity of the product,as well as on manufacturing related issues. By adjusting thicknesses inany of the three dielectric layers and the two silver layers, it ispossible to produce an entire pallet of colors. The goal in this EXAMPLEwas to produce a relatively neutral appearing color.

The maximum thickness of the titanium primer is limited by its effect oncoating hardness and optics as described elsewhere, and its minimumthickness is determined by its degree of effectiveness in protectingsilver during the multi-layer deposition process. Since the coatedproduct of this example is not intended for tempering, lesser thicknessof titanium primer is needed than in EXAMPLE 1. Limits on the thicknessof the titanium dioxide overcoat as described in EXAMPLE 1 apply to thisexample as well.

EXAMPLE 4 Zinc-Aluminum Oxide Metal Contact Film Part

The coating of this example was deposited on a 12 inch×12 inch (30.48cm×30.48 cm) clear float glass substrate using an Airco ILS1600 coater.The coating consisted of the following layer sequence: glass|zinc-tinoxide|zinc-aluminum suboxide|silver titanium|zinc-tin oxide|titaniumoxide. Pressure was maintained at 4 mTorr during the deposition of alllayers of this coating.

The support film-part contiguous to the glass substrate was sputtered ina 65%O₂ -35%Ar atmosphere by multiple passes of the substrate under atin-zinc alloy target at 2 kW of power. Total thickness of the resultingzinc stannate was approximately 390 Angstroms.

The metal-contact film-part was sputtered from a zinc-aluminum oxideceramic target in a pure Ar atmosphere at 0.2 kW of power. This methodof sputtering results in a partially reduced layer of zinc-aluminumoxide that is less transparent than a fully oxidized layer of similarthickness. The thickness of this layer was approximately 75 Angstroms,but other thicknesses were also used with the similar results (e.g.,15-100 Angstroms).

The silver and titanium films were also sputtered in pure argonatmospheres and were approximately 130 Angstroms and 21 Angstroms thick,respectively.

The zinc stannate above the titanium primer was deposited in the samemanner as the first zinc stannate layer and had a similar thickness.

Finally, the titanium oxide overcoat was deposited reactively in a 65%O₂-35%Ar atmosphere using multiple passes of the substrate under atitanium target at 6.5 kW of power. The thickness of this layer wasapproximately 45 Angstroms.

This coating passed the shear resistance test, and had a low post-temperhaze. As a result of tempering, its transmission increased from 76.6% to84% and its resistance went from 5.3 ohm/sq to 3.8 ohm/sq., while itsemissivity decreased, from an initial value of 0.09, to 0.07.

The above examples are offered to illustrate the present invention.Various modifications are included.

For example, other coating compositions are within the scope of thepresent invention. Depending on the proportions of zinc and tin when azinc/tin alloy is sputtered, films of oxide of zinc and tin may deviatesignificantly from exact stoichiometry of zinc stannate (i.e.,deviations from a 2:1 Zn:Sn atom ratio). While deposited as titaniummetal, after deposition the primer layers may comprise titanium metal invarious states of oxidation. In the claims which follow, the titaniumthicknesses, as given, are referenced to the XRF method, as describedabove, in order that thickness variations due to varying degrees ofoxidation are factored out. Other metals such as zirconium and chromiumare also useful as primers in accordance with the present invention.

The thicknesses of the various layers are limited primarily by thedesired optical properties such as transmittance, emissivity or color.

Process parameters such as pressure and concentration of gases may bevaried over a broad range, as long as the intended structures of eachlayer, as described in the body of this text, are realized.

Protective coatings of other chemically resistant materials may bedeposited as either metal or oxides.

Other metal-contact films, i.e. other materials or same materials inother forms, that promote a preferentially (as opposed to randomly)oriented growth of the crystal grains within the silver film may also beused.

Thus, it is to be understood that the above are preferred modes ofcarrying-out the invention and that various changes and alterations canbe made without departing from the spirit and broader aspects of theinvention as defined by the claims set forth below and by the range ofequivalency allowed by law.

What is claimed is:
 1. A high transmittance, low emissivity coatedarticle comprising:a. a transparent, nonmetallic substrate; b. adielectric, antireflective base film overlying the substrate, the basefilm including a zinc-tin oxide support film-part overlying thesubstrate and a crystalline metal-contacting film-part selected from thegroup consisting of indium tin oxide, zinc-aluminum oxide, zinc oxideand mixtures thereof overlying the support film-part; c. a metallicreflective film deposited on the crystalline metal-contacting film-partof the base film, the metallic film having two levels of electricalresistivity, one level being lower than the other; d. a primer filmoverlying the metallic reflective film; and e. a dielectric,antireflective film overlying the primer film;wherein themetal-contacting film-part directs said metallic film to the lower ofsaid two levels.
 2. A coated article as claimed in claim 1 furthercomprising an exterior protective overcoat layer overlying thedielectric antireflective film.
 3. A coated article as claimed in claim2 wherein the transparent, nonmetallic substrate is glass, the supportfilm-part is a zinc stannate film, the crystalline metal-contactingfilm-part is a zinc oxide film, the metallic reflective film is a silverfilm, the primer film is deposited as titanium metal having a thicknessin the range of about 22 to 30 Angstroms, the dielectric, antireflectivefilm is a zinc stannate film, and the exterior protective overcoat layeris a titanium oxide film.
 4. A high transmittance, low emissivity coatedarticle comprising:a. a transparent, nonmetallic substrate; b. a firstdielectric, antireflective base film overlying the substrate, the firstbase film including a zinc-tin oxide support film-part overlying thesubstrate and a crystalline metal-contacting film part selected from thegroup consisting of indium tin oxide, zinc-aluminum oxide and zinc oxideoverlying the support film-part; c. a first metallic reflective filmdeposited on the crystalline metal-contacting film-part of the firstbase film, the metallic film having two levels of electricalresistivity, one level being lower than the other; d. a first primerfilm overlying the first metallic reflective film; e. a seconddielectric, antireflective base film overlying the first primer film,the second base film including a zinc-tin oxide support film-partoverlying the first primer film and a crystalline metal-contactingfilm-part selected from the group consisting of indium tin oxide, zincaluminum oxide and zinc oxide overlying the support film-part; f. asecond metallic reflective film deposited on the crystallinemetal-contacting film-part of the second base film, the metallic filmhaving two levels of electrical resistivity, one level being lower thanthe other; g. a second primer film overlying the second metallicreflective film; and h. a dielectric, antireflective film overlying thesecond primer film;wherein the metal-contacting film-part of the firstbase film directs the first metallic film to the lower of said twolevels and the metal-contacting film-part of the second base filmdirects the second metallic film to the lower of said two levels.
 5. Acoated article as claimed in claim 4 further comprising an exteriorprotective overcoat layer overlying the dielectric, antireflective film.6. A coated article as claimed in claim 5 wherein the transparent,nonmetallic substrate is glass, the support film-part of the first basefilm is a zinc stannate film, the crystalline metal-contacting film-partof the first base film is a zinc oxide film; the first metallicreflective film is a silver film, the first primer film is deposited astitanium metal having a thickness of 22 to 30 Angstroms, the supportfilm-part of the second base film is a zinc stannate film, thecrystalline metal-contacting film-part of the second base film is a zincoxide film, the second metallic reflective film is a silver film, thesecond primer film is deposited as titanium metal having a thickness of22 to 30 Angstroms, the dielectric, antireflective film deposited on thesecond primer film is a zinc stannate film, and the exterior protectiveovercoat layer is a titanium oxide film.
 7. A high transmittance, lowemissivity coated article comprising:a. a transparent, nonmetallicsubstrate; b. a first dielectric, antireflective base film overlying thesubstrate, the first base film including a zinc-tin oxide supportfilm-part overlying the substrate and a crystalline metal-contactingfilm-part selected from the group consisting of indium tin oxide,zinc-aluminum oxide and zinc oxide overlying the support film-part; c. afirst metallic reflective film deposited on the crystallinemetal-contacting film-part of the first base film, the metallic filmhaving two levels of electrical resistivity, one level being lower thanthe other; d. a first primer film overlying the first metallicreflective film; e. a second dielectric, antireflective base filmoverlying the first primer film, the second base film including acrystalline metal-contacting film-part selected from the groupconsisting of indium tin oxide, zinc aluminum oxide and zinc oxideoverlying a support film-part, wherein the support film-part is furthercomprised of a first layer of a zinc oxide film overlying the firstprimer film and a second layer of a zinc stannate film overlying thefirst layer of said support film-part; f. a second metallic reflectivefilm deposited on the crystalline metal-contacting film-part of thesecond base film, the metallic film having two levels of electricalresistivity, one level being lower than the other; g. a second primerfilm overlying the second metallic reflective film; and h. a dielectric,antireflective film overlying the second primer film wherein thedielectric, antireflective film includes a first layer of a zinc oxidefilm overlying the primer film and a second layer of a zinc stannatefilm overlying the first zinc oxide layer of the dielectric,antireflective film;wherein the metal-contacting film-part of the firstbase film directs the first metallic film to the lower of said twolevels and the metal-contacting film-part of the second base filmdirects the second metallic film to the lower of said two levels.
 8. Acoated article as claimed in claim 7 further comprising an exteriorprotective overcoat layer overlying the dielectric antireflective film.9. A coated article as claimed in claim 8 wherein the transparent,nonmetallic substrate is glass, the support film-part of the first basefilm is a zinc stannate film, the crystalline metal-contacting film-partof the first base film is a zinc oxide film, the first metallicreflective film is a silver film, the first primer film is deposited astitanium metal having a thickness of 8 to 12 Angstroms, the secondmetallic reflective film is a silver film, the second primer film isdeposited as titanium metal having a thickness of 8 to 12 Angstroms, andthe exterior protective overcoat layer is a titanium oxide film.
 10. Amethod for making a high transmittance, low emissivity coated articlecomprising the steps of:a. selecting a transparent, nonmetallicsubstrate; b. depositing a dielectric, antireflective base film over thesubstrate, the base film including a zinc-tin oxide support film-partoverlying the substrate and a crystalline metal-contacting film-partselected from the group consisting of indium tin oxide, zinc-aluminumoxide and zinc-oxide overlying the support film-part; c. depositing ametallic reflective film on the crystalline metal-contacting film-partof the base film, the metallic film having two levels of electricalresistivity, one level being lower than the other; d. depositing aprimer film over the metallic reflective film; and e. depositing adielectric, antireflective film over the primer film;wherein themetal-contacting film-part directs said metallic film to the lower ofsaid two levels.
 11. A method according to claim 10 further comprisingthe step of depositing an exterior protective overcoat layer over thedielectric antireflective film.
 12. A method according to claim 11wherein the transparent, nonmetallic substrate is glass, the supportfilm-part is a zinc stannate film, the crystalline metal-contactingfilm-part is a zinc oxide film, the metallic reflective film is a silverfilm, the primer film is deposited as titanium metal having a thicknessof 22 to 30 Angstroms, the dielectric, antireflective film is a zincstannate film, and the exterior protective overcoat layer is a titaniumoxide film.
 13. A method for making a high transmittance, low emissivitycoated article comprising the steps of:a. selecting a transparent,nonmetallic substrate; b. depositing a first dielectric, antireflectivebase film over the substrate, the first base film including a zinc-tinoxide support film-part overlying the substrate and a crystallinemetal-contacting film-part selected from the group consisting of indiumtin oxide, zinc aluminum oxide and zinc oxide overlying the supportfilm-part; c. depositing a first metallic reflective film on thecrystalline metal-contacting film-part of the first base film, themetallic film having two levels of electrical resistivity, one levelbeing lower than the other; d. depositing a first primer film on thefirst metallic reflective film; e. depositing a second dielectric,antireflective base film over the first primer film, the second basefilm including a zinc-tin oxide support film-part overlying the firstprimer film and a crystalline metal-contacting film-part selected fromthe group consisting of indium tin oxide, zinc-aluminum oxide and zincoxide overlying the support film-part; f. depositing a second metallicreflective film on the crystalline metal-contacting film-part of thesecond base film, the metallic film having two levels of electricalresistivity, one level being lower than the other; g. depositing asecond primer film over the second metallic reflective film; and h.depositing a dielectric, antireflective film over the second primerfilm;wherein the metal-contacting film-part of the first base filmdirects the first metallic film to the lower of said two levels and themetal-contacting film-part of the second base film directs the secondmetallic film to the lower of said two levels.
 14. A method according toclaim 13 further comprising the step of depositing an exteriorprotective overcoat layer over the dielectric, antireflective film. 15.A method according to claim 14 wherein the transparent, nonmetallicsubstrate is glass, the support film-part of the first base film is azinc stannate film, the crystalline metal-contacting film-part of thefirst base film is a zinc oxide film; the first metallic reflective filmis a silver film, the first primer film is deposited as titanium metalhaving a thickness of 22 to 30 Angstroms, the support film-part of thesecond base film is a zinc stannate film, the crystallinemetal-contacting film-part of the second base film is a zinc oxide film,the second metallic reflective film is a silver film, the second primerfilm is deposited as titanium metal having a thickness of 22 to 30Angstroms, the dielectric, antireflective film deposited on the secondprimer film is a zinc stannate film, and the exterior protectiveovercoat layer is a titanium oxide film.
 16. A method for making a hightransmittance, low emissivity coated article comprising the steps of:a.selecting a transparent, nonmetallic substrate; b. depositing a firstdielectric, antireflective base film over the substrate, the first basefilm including a zinc-tin oxide support film-part overlying thesubstrate and a crystalline metal-contacting film-part selected from thegroup consisting of indium tin oxide, zinc-aluminum oxide and zinc oxideoverlying the support film part; c. depositing a first metallicreflective film on the crystalline metal-contacting film-part of thefirst base film, the metallic film having two levels of electricalresistivity, one level being lower than the other; d. depositing a firstprimer film over the first metallic reflective film; e. depositing asecond dielectric, antireflective base film over the first primer film,the second dielectric antireflective base film including a crystallinemetal-contacting film-part selected from the group consisting of indiumtin oxide, zinc-aluminum oxide and zinc oxide overlying a supportfilm-part, wherein the support film-part is further comprised of a firstlayer of a zinc oxide film overlying the first primer film and a secondlayer of a zinc stannate film overlying the first layer of said supportfilm-part; f. depositing a second metallic reflective film on thecrystalline metal-contacting film-part of the second base film, themetallic film having two levels of electrical resistivity, one levelbeing lower than the other; g. depositing a second primer film over thesecond metallic reflective film; and h. depositing a dielectric,antireflective film over the second primer film wherein the dielectric,antireflective film includes a first layer of a zinc oxide filmdeposited over the primer film and a second layer of a zinc stannatefilm deposited on the first zinc oxide layer of the dielectric,antireflective film;wherein the metal-contacting film-part of the firstbase film directs the first metallic film to the lower of said twolevels and the metal-contacting film-part of the second base filmdirects the second metallic film to the lower of said two levels.
 17. Amethod according to claim 16 further comprising the step of depositingan exterior protective overcoat layer over the dielectric antireflectivefilm.
 18. A method according to claim 17 wherein the transparent,nonmetallic substrate is glass, the support film-part of the first basefilm is a zinc stannate film, the crystalline metal-contacting film-partof the first base film is a zinc oxide film, the first metallicreflective film is a silver film, the first primer film is deposited astitanium metal having a thickness of 8 to 12 Angstroms, the secondmetallic reflective film is a silver film, the second primer film isdeposited as titanium metal having a thickness of 8 to 12 Angstroms, andthe exterior protective overcoat layer is a titanium oxide film.
 19. Themethod of claim 10 further comprising the step of subjecting the coatedarticle to a heat treatment.
 20. The method of claim 19 wherein thenonmetallic substrate is glass and said heat treatment is a temperingheat treatment to temper said glass substrate.
 21. The method of claim13 further comprising the step of subjecting the coated article to aheat treatment.
 22. The method of claim 21 wherein the nonmetallicsubstrate is glass and said heat treatment is a heat treatment to tempersaid glass substrate.
 23. A high transmittance, low emissivity coatedarticle comprising:a. a transparent, nonmetallic substrate; b. adielectric, antireflective base film overlying the substrate, the basefilm including a support film-part overlying said substrate and acrystalline metal-contact film-part overlying the support film-part; andc. a metallic-reflective film on the crystalline metal-contactfilm-part, the metallic film having two levels of electricalresistivity, one level being lower than the other;wherein the supportfilm-part is chemically and thermally more durable than said crystallinemetal-contact film-part, said support film-part bonding said crystallinemetal-contact film-part to said substrate and wherein said crystallinemetal-contact film-part directs said metallic film to the lower of saidtwo resistivity levels.
 24. The high transmittance, low emissivitycoated article of claim 23 wherein said base film having said metallicreflective film deposited thereon is included on a multi-layer stackdeposited on said substrate.
 25. The article of claim 23 wherein thesupport film-part includes an oxide of zinc and tin.
 26. The article ofclaim 24 wherein the metal-contact film-part is selected from the groupconsisting of indium tin oxide, zinc-aluminum oxide and zinc oxide. 27.The article according to claim 1 wherein said base film is deposited onsaid substrate.
 28. The article according to claim 4 wherein said firstbase film is deposited on said substrate.
 29. The article according toclaim 7 wherein said first base film is deposited on said substrate. 30.The method according to claim 10 wherein said base film is deposited onsaid substrate.
 31. The method of claim 13 wherein said first base filmis deposited on said substrate.
 32. The method of claim 16 wherein saidfirst base film is deposited on said substrate.
 33. A hightransmittance, low emissivity coated article comprising:a. atransparent, nonmetallic substrate; b. a first dielectric,antireflective base film overlying the substrate, the first base filmincluding a zinc-tin oxide support film-part overlying the substrate anda crystalline metal-contacting film part selected from the groupconsisting of indium tin oxide, zinc-aluminum oxide and zinc oxideoverlying the support film-part; c. a first metallic reflective filmdeposited on the crystalline metal-contacting film-part of the firstbase film, the metallic film having two levels of electricalresistivity, one level being lower than the other; d. a first primerfilm overlying the first metallic reflective film; e. a seconddielectric, antireflective base film overlying the first primer film; f.a second metallic reflective film overlying the second base film; g. asecond primer film overlying the second metallic reflective film; and h.a dielectric, antireflective film overlying the second primerfilm;wherein the metal-contacting film-part of the first base filmdirects the first metallic film to the lower of said two levels.
 34. Thecoated article according to claim 33 wherein the first base film isdeposited on the substrate.
 35. A high transmittance, low emissivitycoated article comprising:a. a transparent, nonmetallic substrate; b. afirst dielectric, antireflective base film overlying the substrate; c. afirst metallic reflective film overlying the first base film; d. a firstprimer film overlying the first metallic reflective film; e. a seconddielectric, antireflective base film overlying the first primer film,the second base film including a zinc-tin oxide support film-partoverlying the first primer film and a crystalline metal-contactingfilm-part selected from the group consisting of indium tin oxide, zincaluminum oxide and zinc oxide overlying the support film-part; f. asecond metallic reflective film deposited on the crystallinemetal-contacting film-part of the second base film, the metallic filmhaving two levels of electrical resistivity, one level being lower thanthe other; g. a second primer film overlying the second metallicreflective film; and h. a dielectric, antireflective film overlying thesecond primer film;wherein the metal-contacting film-part of the secondbase film directs the second metallic film to the lower of said twolevels.
 36. A method for making a high transmittance, low emissivitycoated article comprising the steps of:a. selecting a transparent,nonmetallic substrate; b. depositing a first dielectric, antireflectivebase film on the substrate, the first base film including a zinc-tinoxide support film-part overlying the substrate and a crystallinemetal-contacting film-part selected from the group consisting of indiumtin oxide, zinc aluminum oxide and zinc oxide overlying the supportfilm-part; c. depositing a first metallic reflective film on thecrystalline metal-contacting film-part of the first base film, themetallic film having two levels of electrical resistivity, one levelbeing lower than the other; d. depositing a first primer film over thefirst metallic reflective film; e. depositing a second dielectric,antireflective base film over the first primer film; f. depositing asecond metallic reflective film over the second base film; g. depositinga second primer film over the second metallic reflective film; and h.depositing a dielectric, antireflective film over the second primerfilm;wherein the metal-contacting film-part of the first base filmdirects the first metallic film to the lower of said two levels.
 37. Themethod according to claim 36 wherein the first base film is deposited onthe substrate.
 38. A method for making a high transmittance, lowemissivity coated article comprising the steps of:a. selecting atransparent, nonmetallic substrate; b. depositing a first dielectric,antireflective base film over the substrate; c. depositing a firstmetallic reflective film over the first base film; d. depositing a firstprimer film over the first metallic reflective film; e. depositing asecond dielectric, antireflective base film over the first primer film,the second base film including a zinc-tin oxide support film-partoverlying the first primer film and a crystalline metal-contactingfilm-part selected from the group consisting of indium tin oxide,zinc-aluminum oxide and zinc oxide overlying the support film-part; f.depositing a second metallic reflective film on the crystallinemetal-contacting film-part of the second base film, the metallic filmhaving two levels of electrical resistivity, one level being lower thanthe other; g. depositing a second primer film over the second metallicreflective film; and h. depositing a dielectric, antireflective filmover the second primer film;wherein the metal-contacting film-part ofthe second base film directs the second metallic film to the lower ofsaid two levels.